Generally, a crankshaft is rotatably supported by a main bearing installed in a crank case of an engine, and the crankshaft is a device for changing linear motion of a piston into rotary motion through a connecting rod in the power stroke of each cylinder.
The crankshaft consists of a crank pin, a crank arm, a crank journal, etc. that are integrally formed, and a balance weight is attached to the crank arm in order to maintain a rotational balance.
Since a center of the crank journal is eccentric to a center of the crank pin, the crankshaft does not maintain balance while rotating, and a rotational mass moment and a reciprocal mass moment are generated.
However, since the generated moment is accompanied by a complicated vibration, the balance weight is applied to smoothly operate an engine and to maintain balance of a balance shaft.
Recently, since a distance between the piston and the crankshaft has been shortened and it is necessary to maintain a gap between the piston and the balance weight, an exterior diameter of the balance weight has decreased, thus an entire rotatory balance may deteriorate.
Accordingly, in order to stably maintain the gap between the piston and the balance weight and to normally maintain a function of the balance weight, research on a shape of the balance weight is being carried out.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.